The present invention relates to an optical film, an image display device, and diethynylfluorene used for a forming material of the optical film, and a polymer containing the diethynylfluorene.
A retardation film is an optical film for compensating a liquid crystal cell or the like, which is utilized for, for example, realizing a wider viewing angle or the like of a liquid crystal display. The retardation of the retardation film depends on wavelength, and the wavelength dispersion of the retardation is roughly classified into the following three kinds. The first exhibits wavelength dispersion such that a retardation value is larger on the shorter wavelength side (hereinafter referred to as ‘normal dispersion’), the second exhibits wavelength dispersion such that a retardation value scarcely changes ranging from the short wavelength side to the long wavelength side (hereinafter referred to as ‘flat dispersion’), and the third exhibits wavelength dispersion such that a retardation value is smaller on the shorter wavelength side (hereinafter referred to as ‘inverse dispersion’).
Here, the normal dispersion and the inverse dispersion are optical properties such that the wavelength dependence of the retardation is large, and the flat dispersion is optical property such that the wavelength dependence of the retardation is small.
Among such three kinds of retardation films, as the film exhibiting the flat dispersion, a norbornene-based film (for example, trade name: ARTON FILM, manufactured by JSR Corporation) obtained by film-forming and drawing a norbornene-based resin has been conventionally utilized. However, the norbornene-based film is so comparatively thick as approximately 60 to 80 μm that, accordingly, thin and lighter weight of an optical member can't be achieved.
On the other hand, it is known that polyimide exhibits predetermined retardation by coating on a base material (Patent Document 1). Thus, a retardation film containing polyimide may be formed comparatively thinly. However, polyimide ordinarily exhibits the normal dispersion, so that a retardation film using this does not exhibit the flat dispersion.    [Patent Document 1] Japanese translation of PCT international application No. 2000-511296